Project Summary Humans display a set of perceptual biases to social stimuli that are apparent early in life and set the stage for subsequent social cognitive development. However, the degree to which different individuals show these perceptual biases and are ultimately successful at advanced social cognitive processes varies, and in extreme cases may be indicative of disorders like autism. Successful social functioning has strong links to health outcomes; therefore discovering the neurobiological factors that contribute to healthy social development is a critical health goal across many disciplines. Using an individual-differences approach, this proposal aims to link epigenetic variability of the oxytocin system to variability in neural noise profiles and social behavioral outcomes during the first year of life. Measures of neural noise capitalize upon the inherently fluctuating nature of the brain to quantify moment-to-moment variability and complexity in neural signals. This work has revealed that neural noise increases during development, is positively associated with behavioral performance, and linked to neurodevelopmental disorders like autism. In addition to its traditionally understood role in regulating social behaviors, oxytocin acts as a neuromodulator to increase the firing rate of fast-spiking interneurons, which balances neural inhibition and excitation and regulates the level of neural noise. Therefore, early-life variability in the oxytocin system may trigger variable levels of neural noise and ultimately set differential developmental trajectories. This proposal tests the hypothesis that neural noise plays a predominant role in establishing the saliency of social information early in life through a process governed by the endogenous oxytocin system. Infants will undergo electroencephalography to assess the level of neural noise at the ages of 4, 8, and 12 months. To establish whether social stimuli evoke unique neural noise profiles, neural noise will be assessed in response to both social and non-social stimuli across visual and auditory modalities. Infants will also participate in an eye-tracking paradigm to assess the degree to which social information captures attention, and a free- play session to quantify overt, developmentally appropriate social behaviors. Finally, infants will provide a saliva sample for the assessment of DNA methylation of the oxytocin receptor (OXTR). The proposed research is directly in line with the mission of the NICHD, as the results of this study will provide insight into the infant's developing brain and may identify molecular and neural signatures reflective of differential developmental trajectories. These neurobiological markers of normative social development may be used to identify individuals at risk for atypical development before overt clinical behaviors manifest.